(Portland, OR) -- Volunteers with the Oregon Zoo have released 11 endangered northwestern pond turtles into the Columbia River Gorge. The turtles were nearly driven to extinction by non-native American bullfrogs. The Zoo raises the turtles until they're large enough to survive against the bullfrogs and then releases them into ponds. Over the last two decades more than 16-hundred turtles have been released into the Gorge.